In order to prevent the leakage of a gas from an internal space communicating with a compression chamber inside a cylinder in a cylinder head of a compressor, the compressor includes a suction valve pressing portion that presses a suction valve so that the suction valve provided in the internal space of the cylinder head dos not slip off through a suction-side head opening, the suction valve pressing portion includes a suction valve pressing and inserting portion that is inserted into the cylinder head through the suction-side head opening, the outer peripheral surface of the suction valve pressing and inserting portion is provided with an annular suction valve pressing groove portion, a suction-side O-ring is attached into the suction valve pressing groove portion, and a suction-side backup ring that suppresses the movement of the suction-side O-ring toward the suction-side head opening is disposed at a position near the suction-side head opening of the suction-side O-ring inside the suction valve pressing groove portion.